1. Field of the Invention
The present invention is related to processing of dielectric or semiconductor materials. More particularly, the invention is related to releasing a dielectric or semiconductor wafer from an electrostatic chuck.
2. Description of the Related Art
During the process of wafer processing or glass processing, an electrostatic chuck (ESC) is used to clamp the semiconductor or dielectric wafer to a metal holder. The ESC operates like a capacitor in that a static charge is built up between the wafer and the metal holder to clamp or secure the wafer on the metal holder. The process of semiconductor or dielectric processing deposits a substantial amount of power on the wafer. In order to cool the wafer during processing, a heat transfer medium is needed to transfer heat from the wafer to a heat sink. The heat sink is a metal holder which is water cooled. The heat transfer medium is a gas such as helium which is capable of transferring heat from the wafer to the water-cooled metal holder. The ESC is the preferred clamping device to hold the wafer against the metal holder. Upon completion of the processing, the wafer must be removed from the metal holder. A residual sticking force remains between the ESC and the wafer after the clamping force has been turned off. The process of removing the wafer due to this sticking force is referred to as “dechucking” or declamping the wafer. The dechucking process is complicated by the variation in dechucking values for each individual ESC. Therefore, the dechucking values used for one ESC do not necessarily work for another ESC, even if each ESC is made by the same manufacturer using the same materials. Additionally, a single ESC has electrical properties that depend on temperature, so the dechucking values at one temperature do not necessarily work for the same ESC at a different temperature. In addition to variations from one chuck to another, and variations of a given chuck with temperature, the optimum dechucking conditions (the voltage offsets more than the pole-to-pole voltage magnitudes) can also depend on the type of wafer being processed and even on the recipe used to do the processing.
Therefore, a system and method for dechucking is needed that takes into consideration the electrical properties for each ESC.